Accessing Linux build worker via Secure Shell

AppVeyor starts every build on clean dedicated build worker VM. Sometimes the best way to troubleshoot a broken build is looking into Linux VM via Secure Shell (SSH). During the build, you have full “root” access to that VM.

To enable SSH access during the build, you should configure two environment variables (either in appveyor.yml or on Environment tab of project settings):

  • APPVEYOR_SSH_KEY - public portion of your SSH key, for example ssh-rsa AAAAB3NzaC1yc2EAAAABJQ...6TMCNw==. This variable is mandatory.
  • APPVEYOR_SSH_BLOCK - if set to true, the build will be blocked until ~/build.lock is deleted; otherwise, the build will continue. This variable is optional, with default value false.

Despite the fact appveyor.yml settings take over the UI, environment variables are handled differently, i.e. environment variables defined on UI are merged with those defined in appveyor.yml.

Add the following Bash command at the place where SSH access should be enabled:

curl -sflL 'https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-ssh.sh' | bash -e -

For example, to enable SSH access at the very beginning of the build, during init phase:

environment:
  APPVEYOR_SSH_KEY: <your ssh public key>

init:
  - sh: curl -sflL 'https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-ssh.sh' | bash -e -

SSH connection details for the current build worker will be displayed and build will continue. Displaying SSH connection details during init phase helps troubleshooting stuck builds.

If you need to investigate worker on build finish, add export APPVEYOR_SSH_BLOCK=true to display SSH connection details and pause the build until a special “lock” file on VM user home directory is deleted:

on_finish:
  - sh: export APPVEYOR_SSH_BLOCK=true
  - sh: curl -sflL 'https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-ssh.sh' | bash -e -

SSH session is limited by overall build time (60 min).

Generating SSH key

ssh-keygen

ssh-keygen is available on Linux (Windows Subsystem for Linux on Windows 10) and it comes bundled with Git for Windows and usually located at C:\Program Files\Git\usr\bin\ssh-keygen.exe.

The following command generates 2048-bit RSA key and saves its private and public keys into C:\MyProjects\ssh-key.key and C:\MyProjects\ssh-key.key.pub files respectively:

"C:\Program Files\Git\usr\bin\ssh-keygen.exe" -t rsa -b 2048 -N "" -C appveyor -f /c/MyProjects/ssh-key.key

PuTTYgen

You can generate SSH key using “PuTTYgen” GUI tool which is a part of PuTTY - a free SSH client for Windows. To start PuTTYgen click Windows start menu and type PuTTYgen. Configure the following parameters:

  • Type of key to generate: RSA
  • Number of bits in a generated key: 2048

Click Generate button then save both public and private keys.

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